Thermostatic switch with improved heater assembly and method of assembling same

ABSTRACT

A thermostatically controlled electrical switch having a heater assembly adjacent the thermostatic element. The heater assembly includes ceramic substrate with a resistive coating on the face of the substrate remote from the thermostatic element. First and second spaced conductive contact layers are provided on the resistive coatings. The resistive coatings are connected to exterior terminals via stiff spring elements which have coiled end portions biased into firm electrical contact with the respective contact layers.

United States Patent lnventor Jack W. Grable Lexington, Ky.

Appl. No. 872,446

Filed Nov. 21, 1969 Patented May 18, 1971 Assignee Texas Instruments Incorporated Dallas, Tex.

Continuation of application Ser. No. 566,674, July 20, 1966, now abandoned.

THERMOSTATIC SWITCH WITH IMPROVED HEATER ASSEMBLY AND METHOD OF ASSEMBLING SAME 4 Claims, 14 Drawing Figs.

US. Cl 337/102, 337/107, 337/354 Int. Cl ..H01h 37 54, 37/54, I-IOlh 37/64, l-IOlh 61/013 Field of Search 337/ 102- BIME TAL [56] References Cited UNITED STATES PATENTS 2,268,617 1/1942 Pierce l74/126(.2) 2,448,389 8/1948 Powell 200/129 Primary Examiner-Remard A. Gilheany Assistant Examiner-Dewitt M. Morgan Attorneys-Harold Levine, Edward J. Connors, Jr. and John l A. Hang l ABSTRACT: A thermostatically controlled electrical switch having a heater assembly adjacent the thermostatic element. The heater assembly includes ceramic substrate with a resistive coating on the face of the substrate remote from the thermostatic element. First and second spaced conductive contact layers are provided on the resistive coatings. The resistive coatings are connected to exterior terminals via stiff spring elements which have coiled end portions biased into firm electrical contact with the respective contact layers.

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THERMOSTATIC SWITCH WITH IMPROVED HEATER ASSEMBLY AND METHOD OF ASSEMBLING SAME This is a continuation of application Ser. No. 566,674 filed July 20, 1966 and now abandoned.

This invention relates to thermostatic electrical switches, and with regard to certain more specific features, to switches employing an improved heater.

Among several objects of the invention may be noted the provision of thermostatically controlled electrical switches, particularly the snap-acting type, incorporating improved features of form to save manufacturing costs while preserving the accurate dimensional relationship required for a higher quality product; and incorporating an improved heater which is rugged, durable, easier and less expensive to assemble yet can be operated more efficiently and at higher temperatures than conventional heaters. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, steps and sequence of steps, features of construction and manipulation, and arrangements of parts which will be exemplified in the structures and methods.

hereinafter described, and the scope of which will be indicated in the following claims.

in the accompanying drawings, in which several various possible embodiments of the invention are illustrated:

FIG. 1 is a plan view of a thermostatic switch according to the first embodiment of the instant invention;

FIG. 2 is a cross section taken on line 2-2 of FIG. 1, and showing in solid lines the contacts in closed position and in phantom lines the contacts in open position;

FlG. 3 is a cross section taken on line 3-3 of FIG. 2, and shows details of the heater assembly employed in the device;

FIG. 4 is a fragmentary cross section taken on line 4-4 of FIG. 3, and shows certain features of the heater assembly;

FIG. 5 is a cross section taken on line 5-5 of FIG. 4;

FIG. 6 is a bottom plan view of the movable contact assembly used in this invention;

FIG. 7 is a cross section taken on line 7-7 of FIG. 6;

FIG. 8 is a plan view similar to FIG. 1 of a thermostatic 7 switch according to a second embodiment of the instant invention;

FIG. 9 is a cross section taken on line 9-9 of FIG. 8;

FIG. 10 is across section taken on line 10-10 of FIG. 9;

FIG. 11 is a view similar to FIG. 9, but partly diagrammatic and partly in section and showing the movable contact in engagement with the back stationary contact;

FlG. 12 is a perspective view of the heater assembly partly broken away;

FIG. 13 is a bottom plan view of the back stationary contact mounting assembly; and

FIG. 14 is a cross section taken on line 14-14 of FIG. 13.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Referring to the drawings,and particularly to FIGS. 1-7 and 12, there is shown a thermostatic switch indicated generally by numeral 10. A housing or base member 12 composed of a conventional molded insulating material such as a phenolic resin, is made up with a cup-shaped cylindrical por- 'tion defining cavity 14 therein. Grooves 13 are provided in base 12 to facilitate attachment of cap 16 by staking thereto in a conventional manner. Cap 16, preferably formed of material having hood thermal conductivity to enhance the response of the thermostatic element encloses cavity 14 and is provided with a mounting flange 18. Flange 18 has suitable apertures 20 therein useful for mounting device 10 to support (not shown).

Cap 16 is cup-shaped and has open or closed ends 22 formed with annular seat portions 24 and 26. A bimetallic snap-acting disc '30 is supported on annular seat 24. Base member 12 is telescopically inserted in cap 16 with seat portion 26 of cap 16 receiving the distal wall portion of member 12.

The distal wall portion of member 12 is formed with an annular recess portion which provides a shoulder 32 in which recess a circular disc-shaped guide member 34 is located.

Guide member 34 is composed of insulating material capable of withstanding high temperatures, such as ceramic and is formed with a coaxial bore 36 through which a pin 38 composed of insulating material is slidably inserted. The function of this pin will be described in greater detail infra.

It will be noted (see H0. 11) thatguide member 34 can be formed with cars 33 if desirable, useful in maintaining alignment of the member in the device.

Guide 34 is formed with an annular cut out portion 40 which serves as a seat for heater assembly 42 composed of an annular wafer 43, also of insulating material capable of withstanding high temperatures, such as ceramic. On a surface of the wafer or substrate 43, a thin resistive coating 44 is located. Coating 44 may conveniently be a conventional gold, platinum or silver resistor composition availablerby E. l. du- Pont de Nemours & Co. A preferred resistor composition is Paladium-Silver-Glass Glaze resistor material and can conveniently be applied by screen printing techniques. The paste material is applied with a squeegee through a screen having the desired pattern and is air-dried for approximately an hour to drive off the volatile components. The coating is then fired at 1400 F. for approximately 10 minutes and then air-cooled. A one mil layer has been found to give satisfactory results. The time and temperatures set forth can be varied to a limited extent depending on various factors such as the thickness of the layer.

Contact layers 46 and 48 may be applied on layer 44 in the same manner employing a conductive contact material, such as silver. After air-drying the silver material is fired at 1 100 F. for approximately 10 minutes and air-cooled.

After measuring the resistance of layer 44 if it is found that adjustment is necessary the resistance can be changed by removing a portion of layer 44 by mechanical means such as by a-grit blast.

Two ear portions 50 may be provided in bore 52 of wafer 43 so that alignment of the contact layers '46, 48 will be facilitated during assembly of device 10.-

Guide 34 is formed with two spaced apertures 54 through each of which is inserted a contact spring member 56 composed of a material which has both high electrical conductivity and good spring characteristics. It has been found that a multilayer material is particularly useful for this part, such as a spring steel or stainless steel core with a copper shell bonded theretoflhe steel provides the spring characteristics required to eh'ect a good electrical connection with the contact layers as described below while the copper provides the conductivity and also permits soldering of the members to the terminals also to be described more fully below. End 60 of each contact spring 56 is inserted in recess 58 and guide 34, which recesses are aligned with contact'layers 46 and 48. Elongated distal end portions of ends 60 are biased against contact layers 46 and 48 respectively resulting in a good electrical connection. As best seen in FIGS. 4 and 5, the distal end portions lie flat against the respective contact layers resulting in increased surface area of contact between springs 56 and the contact layers. Heater assembly 42 is locked in place in cutout portion 40 by a ceramic cement 62 of a conventional type. The other end 62 of spring members 56 are threaded through eyelets 66 and attached, as by soldering or welding, to terminal member 70, 72 mounted on base 12.

The main electrical circuit is normally connected to terminals 74, 76 mounted on base 12. Ribs 77 are provided on the base to separate and isolate the terminals. Terminals 74 and 76 are seated in recesses 78 and 80 respectively in base 12. Recesses 78 and 80 are provided with chambers 79 and 81 respectively, which serve to prevent sideway dislocation of the terminals and facilitate locating and tight assembly of terminals 74, 76 to base 12. Chambers are also provided for terminals 70, 72 and 98.

A relatively rigid L-shaped contact support 82, preferably of bronze, is inserted through aperture 83 in base 12, and is connected to terminal 74 atone end thereof by any convenient means such as staking, as shown at 75. The other end '87 of base 12 and attached to terminal 76 in a manner similar to the attachment of member 82 to terminal 74. Movable contact arm 90, preferably of beryllium copperwhich has high electrical conductivity as well as good spring characteristics, is cantilever mounted to the free end of support86, as-by rivet 85. Arm 90 has a dimple 92 formed therein'and alignedwith pin 38. A contact 94 of a good electrically conductive material, such as silver, is mounted on the free end of arm 90. Shield member '96, preferably of copper, overlays contact 94 and protects arm 90 from deleterious effects of arcing.

FIG. 7 shows support 86 in solid and phantom lines indicating that support 86 is bent during assembly to adjust .thezcontact pressure between contacts 84 and 94..

FIG. 2 shows the contacts in closed position in solid lines and in open position in phantom lin'es..lt will be'understood that upon reaching a predeterminedternperature value. disc element 30 will snap. from the solid line position to the phantom line position causing motion to be transferred through pin 38 to dimple 92 of arm 90 thereby separating contacts 84', 94.

The heater assembly 42 permits the utilization of higher temperatures than conventional heater employed in prior art devices due to its particular construction; The contact spring members are in pressure contact and not connected as in prior art devices by a soldered copper lead. This results in several advantages, the heater temperature is not limited by a soldered connection, there is no weak mechanical connection dependent upon the tensile strength-of silverand further, the assembly ofthe device is greatly facilitated.

.The heater assembly is preferably of all ceramicconstruction except resistive layer 44, contact layers 46, 48 and spring members'56. This permits higher heater temperaturesthan other heaters using phenolic type materials.

lt will also be-noted that the stiff spring members 56 facilitate assembly since the ends thereof can readily be guided through the small eyelets 66. It will be obvious that" flexible leads would be more difficult and require a more elaborateassembly operation.

The heater is nonnallyused in the device to reducexthe effective operating temperature differential and operating" time by causing disc 3.010 reach its operating temperature before the ambient temperature would, and to increase'the on" or "off" time by supplying heat to hold thedisctemperature by providing terminal 98 seated in recess portion 100 of base l2recess portion 100 is formed with chamfer 101 for the same reasons set forth supra in relation to terminals 74, 76.-

Back arm support 102, preferably of brass, is inserted through aperture'l04 and connected to terminal 98 as by stak ing. The other endis provided with seating portion 106 used to calibrate and cantilever mount contact arm 108. Contact arm l08is preferably of beryllium copper to provide a flexible member to decreasecontact bounce as well as to transmit the contact pressure force. Contact member 110, of silver or other electrically conductive material, is mounted on the free end of arm .108. Support 102 is bent to get the desired contact pressure between contacts 94 and 110 as indicated in FIG. 14.

As various changes could be made in the above construction and.methods without departing from the scope of the interpreted as illustrative and not in a limiting sense.

Iclaim:

1. An electric switch comprising:

an open ended cup-shaped'housingcomposed of electrical insulating material, the housing havinga bottom wall and sidewalls dependingtherefrom, I

a ledge formed in the sidewalls .and' a disc seated on the ledge, the disc provided with a bore thereth rough;

a cap closing the open of the housing,

a heat responsive thermostaticmember mounted between thecap and the disc, P

a stationarycontact and a movable contact means mounted in the housing between thebottom'wall and the disc, the movable contact'means movable into and out of engagement with thestationary contact,

a motion transfer pin slidablylocated in the bore of the disc transferring motion'from the thermostatic element to the movable contact means,

a first. recessed portion formed in the disc on the thereof closest to the thermostatic element,

a heater assembly mounted in'the'recessed portion, the

heater assembly including a ceramic substrate,

a resistive coating on the face of the substrate remote from the thermostatic element,

first and sccondspaced conductive contact layers on the resistive coatings,

asecond and third recessedportion formed in the disc in alignment'with the first and second conductive contact layer and in communication with the-first recessed portion,

an'apertureextending from each of the second and third recessed portions through thedisc, fourterminalmembers mounted on the bottom wall, one of the terminal members connected to the stationary contact,.thesecond of the terminal members connected to the movable contact means,.the third and fourth terminal members connected respectively to the first and second conductive contact layer, the connection of the latter two terminal members to the conductive contact layers each being effected by a stiff spring element 'having an elongated distal end portion, theelement'extending from the respective terminal member through a respective aperture provided in the sidewall, through the respective aperture in the disc into the respective second and third recessed portion, the spring element biased into approximatelyaa normal direction to thatportion of the element extending through the disc aperture with the distal end portion of the element lying flat'ag ainst the conductive contact layer and in firm electrical connection therewith and the heater assembly cemented into fixed relationship with the disc. 2; A switch according to claim 1' in which the first recessed portionand the substrateare annular in shape.

3. A' thermostatic electrical switch comprising:

a thermostatic element movable from a first configuration to a second configuration in response to predetermined temperature conditions;

electrical contact means movable into and out of engagement in response to-movement of the thermostatic element from one of the said configurations to the other of said configurations;

heater means for providing heat to the thermostatic elemen includingia mounting member having a face which is approximately parallel to the plane inwhich the thermostatic element lies,

a first recess provided in the face,

a substrate,

a resistive coating on one surface of the substrate,

two spaced contact'layers located on the resistive coating, the substrate fixedly mounted in the first recess with'the resistive coating facing away from the thermostatic element,

second and third recesses provided in communication with the first recess and aligned with respective contact layers,

side

5 6 first and second apertures provided "in the mounting through the aperture and generally parallel to the face of member in communication with the second ,and third the mounting member and with the distal end portion of recesses respectively, and the element lying flat against a respective contact layer in a a spring element having an elongated distal end portion infirm electrical C nnection therewith.

serted in each aperture and extendi g i t h second d 5 A switch according to claim 3 in which the portion of the third recesses respectively, the portion of the spring elesphhgelemeht y h th the P e P to the thee f the ment within the recessed area biased into a plane approximoummg member convoluted m Shape mately normalto that portion of the element extending 

1. An electric switch comprising: an open ended cup-shaped housing composed of electrical insulating material, the housing having a bottom wall and sidewalls depending therefrom, a ledge formed in the sidewalls and a disc seated on the ledge, the disc provided with a bore therethrough; a cap closing the open of the housing, a heat responsive thermostatic member mounted between the cap and the disc, a stationary contact and a movable contact means mounted in the housing between the bottom wall and the disc, the movable contact means movable into and out of engagement with the stationary contact, a motion transfer pin slidably located in the bore of the disc transferring motion from the thermostatic element to the movable contact means, a first recessed portion formed in the disc on the side thereof closest to the thermostatic element, a heater assembly mounted in the recessed portion, the heater assembly including a ceramic substrate, a resistive coating on the face of the substrate remote from the thermostatic element, first and second spaced conductive contact layers on the resistive coatings, a second and third recessed portion formed in the disc in alignment with the first and second conductive contact layer and in communication with the first recessed portion, an aperture extending from each of the second and third recessed portions through the disc, four terminal members mounted on the bottom wall, one of the terminal members connected to the stationary contact, the second of the terminal members connected to the movable contact means, the third and fourth terminal members connected respectively to the first and second conductive contact layer, the connection of the latter two terminal members to the conductive contact layers each being effected by a stiff spring element having an elongated distal end portion, the element extending from the respective terminal member through a respective aperture provided in the sidewall, through the respective aperture in the disc into the respective second and third recessed portion, the spring element biased into approximately a normal directioN to that portion of the element extending through the disc aperture with the distal end portion of the element lying flat against the conductive contact layer and in firm electrical connection therewith and the heater assembly cemented into fixed relationship with the disc.
 2. A switch according to claim 1 in which the first recessed portion and the substrate are annular in shape.
 3. A thermostatic electrical switch comprising: a thermostatic element movable from a first configuration to a second configuration in response to predetermined temperature conditions; electrical contact means movable into and out of engagement in response to movement of the thermostatic element from one of the said configurations to the other of said configurations; heater means for providing heat to the thermostatic element including a mounting member having a face which is approximately parallel to the plane in which the thermostatic element lies, a first recess provided in the face, a substrate, a resistive coating on one surface of the substrate, two spaced contact layers located on the resistive coating, the substrate fixedly mounted in the first recess with the resistive coating facing away from the thermostatic element, second and third recesses provided in communication with the first recess and aligned with respective contact layers, first and second apertures provided in the mounting member in communication with the second and third recesses respectively, and a spring element having an elongated distal end portion inserted in each aperture and extending into the second and third recesses respectively, the portion of the spring element within the recessed area biased into a plane approximately normal to that portion of the element extending through the aperture and generally parallel to the face of the mounting member and with the distal end portion of the element lying flat against a respective contact layer in firm electrical connection therewith.
 4. A switch according to claim 3 in which the portion of the spring element lying in the plane parallel to the face of the mounting member is convoluted in shape. 